Using window underlayer structures to protect near field transducers on heat assisted magnetic recording heads

ABSTRACT

A system, according to one embodiment, includes: a near field transducer, a return pole, a main pole, a waveguide adjacent the near field transducer, wherein the waveguide extends away from the near field transducer along a direction perpendicular to a media facing surface, at least one cladding layer adjacent to the waveguide, an underlayer positioned behind the near field transducer with respect to the media facing surface, the underlayer extending away from the near field transducer along the direction perpendicular to the media facing surface, and a fill material at least partially surrounding the underlayer, the waveguide and the at least one cladding layer. The underlayer has a lower coefficient of thermal expansion than the fill material. Other systems, and methods are described in additional embodiments.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/085,875, filed on Mar. 30, 2016, the entirety ofwhich is incorporated by reference herein.

FIELD

The present application relates to data storage systems, and moreparticularly, this invention relates to heat assisted magnetic recordingwrite heads having improved near field transducer (NFT) structureprotection during use and methods for making the same.

BACKGROUND

The heart of a computer is a magnetic disk drive which typicallyincludes a rotating magnetic disk, a slider that has read and writeheads, a suspension arm above the rotating disk and an actuator arm thatswings the suspension arm to place the read and/or write heads overselected data tracks on the rotating disk. The suspension arm biases theslider into contact with the surface of the disk when the disk is notrotating (in some disk drives, there is a load/unload ramp so contactwith the disk does not occur); but, when the disk rotates, air isswirled by the rotating disk adjacent a media facing surface of theslider causing the slider to ride on an air bearing a slight distancefrom the surface of the rotating disk. When the slider rides on the airbearing the write and read heads are employed for writing magneticimpressions to and reading magnetic signal fields from the rotatingdisk. The read and write heads are connected to processing circuitrythat operates according to a computer program to implement the writingand reading functions.

The ongoing quest for higher storage bit densities in magnetic mediaused in disk drives has reduced the size (volume) of data cells to thepoint where the cell dimensions are limited by the grain size of themagnetic material. Although grain size can be reduced further, there isconcern that data stored within the cells is no longer thermally stable,as random thermal fluctuations at ambient temperatures are sufficient toerase data. This state is described as the superparamagnetic limit,which determines the maximum theoretical storage density for a givenmagnetic medium. This limit may be raised by increasing the coercivityof the magnetic medium or lowering the temperature. Lowering thetemperature is not a practical option when designing hard disk drivesfor commercial and consumer use. Raising the coercivity is a practicalsolution, but requires write heads employing higher magnetic momentmaterials which will make data recording more challenging.

One solution has been proposed, which employs heat to lower theeffective coercivity of a localized region on the magnetic mediumsurface and writes data within this heated region. The data statebecomes “fixed” upon cooling the medium to ambient temperatures. Thistechnique is broadly referred to interchangeably as “heat assistedmagnetic recording”, HAMR, or “thermally assisted (magnetic) recording”,TAR or TAMR. HAMR can be applied to both longitudinal and perpendicularrecording systems, although the highest density state of the art storagesystems are more likely to be perpendicular recording systems. Heatingof the media surface has been accomplished by a number of techniquessuch as focused laser beams or near field optical sources. U.S. Pat. No.6,999,384 to Stancil et al., which is herein incorporated by reference,discloses near field heating of a magnetic medium.

The heat used in HAMR is provided by a plasmonic nanostructure, namelyan NFT, which locally elevates a limited spot on the medium to its Curietemperature of about 600° C. Thus, the thermal and mechanicalreliability of the NFT is important.

However, the thermo-mechanical response of the NFT when exposed to suchhigh temperatures leads to an undesirable protrusion of the plasmonicstructure, thereby making the NFT the minimum fly point over the medium.This increases the risk of damage to the NFT resulting from disk contactduring touchdown and the presence of high thermal asperities duringback-off operations. However, previous attempts to protect NFTs fromsuch damage have been unable to do so with a desired amount ofefficiency.

SUMMARY

A system, according to one embodiment, includes: a near fieldtransducer, a return pole, a main pole, a waveguide adjacent the nearfield transducer, wherein the waveguide extends away from the near fieldtransducer along a direction perpendicular to a media facing surface, atleast one cladding layer adjacent to the waveguide, an underlayerpositioned behind the near field transducer with respect to the mediafacing surface, the underlayer extending away from the near fieldtransducer along the direction perpendicular to the media facingsurface, and a fill material at least partially surrounding theunderlayer, the waveguide and the at least one cladding layer. Theunderlayer has a lower coefficient of thermal expansion than the fillmaterial.

A method, according to another embodiment, includes: applying light to anear field transducer positioned toward a media facing surface of amagnetic head, the magnetic head having: a return pole, a main pole, awaveguide adjacent the near field transducer, wherein the waveguideextends away from the near field transducer along a directionperpendicular to the media facing surface, at least one cladding layeradjacent to the waveguide, an underlayer positioned behind the nearfield transducer with respect to the media facing surface, theunderlayer extending away from the near field transducer along thedirection perpendicular to the media facing surface, and a fill materialat least partially surrounding the underlayer, the waveguide and the atleast one cladding layer. The underlayer has a lower coefficient ofthermal expansion than the fill material. Moreover, upon illumination ofthe near field transducer, a portion of the media facing surface of themagnetic head at the near field transducer exhibits less thermalprotrusion toward a magnetic medium than another portion of the mediafacing surface.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a disk drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., hard disk) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a simplified drawing of a magnetic recording disk drivesystem.

FIG. 2A is a schematic representation in section of a recording mediumutilizing a longitudinal recording format.

FIG. 2B is a schematic representation of a conventional magneticrecording head and recording medium combination for longitudinalrecording as in FIG. 2A.

FIG. 2C is a magnetic recording medium utilizing a perpendicularrecording format.

FIG. 2D is a schematic representation of a recording head and recordingmedium combination for perpendicular recording on one side.

FIG. 2E is a schematic representation of a recording apparatus adaptedfor perpendicular recording separately on both sides of the medium.

FIG. 3A is a cross-sectional view of one particular embodiment of aperpendicular magnetic head with helical coils.

FIG. 3B is a cross-sectional view of one particular embodiment of apiggyback magnetic head with helical coils.

FIG. 4A is a cross-sectional view of one particular embodiment of aperpendicular magnetic head with looped coils.

FIG. 4B is a cross-sectional view of one particular embodiment of apiggyback magnetic head with looped coils.

FIG. 5A is a partial cross sectional view of a thin film perpendicularwrite head according to one embodiment.

FIG. 5B is a partial media facing surface view of the head of FIG. 5Ataken along 5B-5B.

FIG. 6 is a graph of the thermal protrusion experienced across the mediafacing surfaces of magnetic heads according to different embodiments.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofdisk-based storage systems and/or related systems and methods, as wellas operation and/or component parts thereof. Various embodimentsdescribed herein may be able to provide added protection for an NFT. Byselectively implementing underlayers having certain properties, some ofthe embodiments described herein may be able to prevent an NFT frombecoming the minimum fly point over the medium, thereby desirablyproviding greater reliability during recording, as will be described infurther detail below.

In one general embodiment, a system includes: a near field transducer, areturn pole, a main pole, a waveguide adjacent the near fieldtransducer, wherein the waveguide extends away from the near fieldtransducer along a direction perpendicular to a media facing surface, atleast one cladding layer adjacent to the waveguide, an underlayerpositioned behind the near field transducer with respect to the mediafacing surface, the underlayer extending away from the near fieldtransducer along the direction perpendicular to the media facingsurface, and a fill material at least partially surrounding theunderlayer, the waveguide and the at least one cladding layer. Theunderlayer has a lower coefficient of thermal expansion than the fillmaterial.

In another general embodiment, a method includes: applying light to anear field transducer positioned toward a media facing surface of amagnetic head, the magnetic head having: a return pole, a main pole, awaveguide adjacent the near field transducer, wherein the waveguideextends away from the near field transducer along a directionperpendicular to the media facing surface, at least one cladding layeradjacent to the waveguide, an underlayer positioned behind the nearfield transducer with respect to the media facing surface, theunderlayer extending away from the near field transducer along thedirection perpendicular to the media facing surface, and a fill materialat least partially surrounding the underlayer, the waveguide and the atleast one cladding layer. The underlayer has a lower coefficient ofthermal expansion than the fill material. Moreover, upon illumination ofthe near field transducer, a portion of the media facing surface of themagnetic head at the near field transducer exhibits less thermalprotrusion toward a magnetic medium than another portion of the mediafacing surface.

Referring now to FIG. 1, there is shown a disk drive 100 in accordancewith one embodiment of the present invention. As shown in FIG. 1, atleast one rotatable magnetic disk 112 is supported on a spindle 114 androtated by a disk drive motor 118. The magnetic recording on each diskis typically in the form of an annular pattern of concentric data tracks(not shown) on the disk 112.

At least one slider 113 is positioned near the disk 112, each slider 113supporting one or more magnetic read/write heads 121 (e.g., of amagnetic head). As the disk rotates, slider 113 is moved radially in andout over disk surface 122 so that heads 121 may access different tracksof the disk where desired data are recorded and/or to be written. Eachslider 113 is attached to an actuator arm 119 by means of a suspension115. The suspension 115 provides a slight spring force which biasesslider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator 127. The actuator 127 as shown in FIG. 1 may bea voice coil motor (VCM). The VCM comprises a coil movable within afixed magnetic field, the direction and speed of the coil movementsbeing controlled by the motor current signals supplied by controller129.

During operation of the disk storage system, the rotation of disk 112generates an air bearing between slider 113 and disk surface 122 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 115 and supportsslider 113 off and slightly above the disk surface by a small,substantially constant spacing during normal operation. Note that insome embodiments, the slider 113 may slide along the disk surface 122.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 129, such asaccess control signals and internal clock signals. Typically, controlunit 129 comprises logic control circuits, storage (e.g., memory), and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123 and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position slider 113 to the desired data track on disk112. Read and write signals are communicated to and from read/writeheads 121 by way of recording channel 125.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 1 is for representation purposes only.It should be apparent that disk storage systems may contain a largenumber of disks and actuators, and each actuator may support a number ofsliders.

In some embodiments, the disk drive 100 of FIG. 1 may be implemented forHAMR. Accordingly, the disk drive 100 may include an apparatus, e.g.,see 500 of FIG. 5 respectively. Thus, the read/write heads 121 of thedisk drive 100 may operate in combination with an NFT as described indetail below.

With continued reference to the disk drive 100 of FIG. 1, an interfacemay also be provided for communication between the disk drive and a host(integral or external) to send and receive the data and for controllingthe operation of the disk drive and communicating the status of the diskdrive to the host, all as will be understood by those of skill in theart.

In a typical head, an inductive write head includes a coil layerembedded in one or more insulation layers (insulation stack), theinsulation stack being located between first and second pole piecelayers. A gap is formed between the first and second pole piece layersof the write portion by a gap layer at or near a media facing surface ofthe head (sometimes referred to as an air bearing surface in a diskdrive). The pole piece layers may be connected at a back gap. Currentsare conducted through the coil layer, which produce magnetic fields inthe pole pieces. The magnetic fields fringe across the gap at the mediafacing surface for the purpose of writing bits of magnetic fieldinformation in tracks on moving media, such as in circular tracks on arotating magnetic disk.

The second pole piece layer has a pole tip portion which extends fromthe media facing surface to a flare point and a yoke portion whichextends from the flare point to the back gap. The flare point is wherethe second pole piece begins to widen (flare) to form the yoke. Theplacement of the flare point directly affects the magnitude of themagnetic field produced to write information on the recording medium.

FIG. 2A illustrates, schematically, a conventional recording medium suchas used with magnetic disk recording systems, such as that shown inFIG. 1. This medium is utilized for recording magnetic domains in orparallel to the plane of the medium itself. The recording medium, arecording disk in this instance, comprises basically a supportingsubstrate 200 of a suitable non-magnetic material such as glass, with anoverlying coating 202 of a suitable and conventional magnetic layer.

FIG. 2B shows the operative relationship between a conventionalrecording head 204, which may preferably be a thin film head, and alongitudinal recording medium, such as that of FIG. 2A.

FIG. 2C illustrates, schematically, a perpendicular recording headwhere, the orientation of magnetic domains substantially perpendicularto the surface of a recording medium as used with magnetic diskrecording systems, such as that shown in FIG. 1. For such perpendicularrecording the medium typically includes an under layer 212 of a materialhaving a high magnetic permeability. This under layer 212 is thenprovided with an overlying coating 214 of magnetic material preferablyhaving a high coercivity relative to the under layer 212.

FIG. 2D illustrates the operative relationship between a perpendicularhead 218 and a recording medium. The recording medium illustrated inFIG. 2D includes both the high permeability under layer 212 and theoverlying coating 214 of magnetic material described with respect toFIG. 2C above. However, both of these layers 212 and 214 are shownapplied to a suitable substrate 216. Typically there is also anadditional layer (not shown) called an “exchange-break” layer or“interlayer” between layers 212 and 214.

In this structure, the magnetic lines of flux extending between thepoles of the perpendicular head 218 loop into and out of the overlyingcoating 214 of the recording medium with the high permeability underlayer 212 of the recording medium causing the lines of flux to passthrough the overlying coating 214 in a direction generally perpendicularto the surface of the medium to record information in the overlyingcoating 214 of magnetic material preferably having a high coercivityrelative to the under layer 212 in the form of magnetic domains havingtheir axes of magnetization substantially perpendicular to the surfaceof the medium. The flux is channeled by the soft underlying coating 212back to the return pole of the head 218.

FIG. 2E illustrates a similar structure in which the substrate 216carries the layers 212 and 214 on each of its two opposed sides, withsuitable recording heads 218 positioned adjacent the outer surface ofthe magnetic coating 214 on each side of the medium, allowing forrecording on each side of the medium.

FIG. 3A is a cross-sectional view of a perpendicular magnetic head. InFIG. 3A, helical coils 310 and 312 are used to create magnetic flux inthe stitch pole 308, which then delivers that flux to the main pole 306.Coils 310 indicate coils extending out from the page, while coils 312indicate coils extending into the page. Stitch pole 308 may be recessedfrom the media facing surface 318. Insulation 316 surrounds the coilsand may provide support for some of the elements. The direction of themedia travel, as indicated by the arrow to the right of the structure,moves the media past the lower return pole 314 first, then past thestitch pole 308, main pole 306, trailing shield 304 which may beconnected to the wrap around shield (not shown), and finally past theupper return pole 302. Each of these components may have a portion incontact with the media facing surface 318. The media facing surface 318is indicated across the right side of the structure.

Perpendicular writing is achieved by forcing flux through the stitchpole 308 into the main pole 306 and then to the surface of the diskpositioned toward the media facing surface 318.

FIG. 3B illustrates a piggyback magnetic head having similar features tothe head of FIG. 3A. Shield 304 and return pole 314 flank the stitchpole 308 and main pole 306. Also sensor shields 322, 324 are shown. Theread sensor 326 is typically positioned between the sensor shields 322,324.

FIG. 4A is a schematic diagram of one embodiment which uses looped coils410, sometimes referred to as a pancake configuration, to provide fluxto the stitch pole 408. The stitch pole then provides this flux to themain pole 406. In this orientation, the lower return pole is optional.Insulation 416 surrounds the coils 410, and may provide support for thestitch pole 408 and main pole 406. The stitch pole may be recessed fromthe media facing surface 418. The direction of the media travel, asindicated by the arrow to the right of the structure, moves the mediapast the stitch pole 408, main pole 406, trailing shield 404 which maybe connected to the wrap around shield (not shown), and finally past theupper return pole 402 (all of which may or may not have a portion incontact with the media facing surface 418). The media facing surface 418is indicated across the right side of the structure. The trailing shield404 may be in contact with the main pole 406 in some embodiments.

FIG. 4B illustrates another type of piggyback magnetic head havingsimilar features to the head of FIG. 4A including looped coils 410,which loops around to form looped coils 412. Also, sensor shields 422,424 are shown, with the upper sensor shield 422 spaced from the writerby a nonmagnetic layer 414. The sensor 426 is typically positionedbetween the sensor shields 422, 424.

In FIGS. 3B and 4B, an optional heater 328, 428, respectively, is shownaway from the media facing surface of the magnetic head. A heater 328,428 may also be included in the magnetic heads shown in FIGS. 3A and 4A.The position of this heater may vary based on design parameters such aswhere the protrusion is desired, coefficients of thermal expansion ofthe surrounding layers, etc.

As previously mentioned, HAMR, or equivalently TAR, is a method ofrecording information onto a magnetic recording medium. One generalmotivation for this invention relates to the design of a recesseddielectric waveguide and integration with a near-field opticaltransducer for HAMR. The waveguide core may be optimally recessed by adistance from the transducer and this space may be filled with low indexdielectric material, leading to significant enhancement of the opticalefficiency. In one preferred embodiment, the low index dielectricmaterial in the recessed space may be deposited after fabrication of thenear-field transducer using an anisotropic deposition followed bydeposition of the high index core material.

According to some embodiments, for HAMR to be effective, it may bebeneficial to confine heat to about a single data track which may beapproximately 40 nm wide or smaller. Candidate near-field opticalsources typically use a low-loss metal (Au, Ag, Al, Cu, etc.) shaped insuch a way as to concentrate surface charge motion at a tip apex locatedat the slider media facing surface when light is incident. Oscillatingtip charge may create an intense near-field pattern, heating the disk.Sometimes, the metal structure can create resonant charge motion(surface plasmons) to further increase intensity and disk heating. Forexample, when polarized light is aligned with the corner of atriangular-shaped gold plate, an intense near field pattern may becreated at that corner. Resonant charge motion may occur by adjustingthe triangle size to match a surface plasmon frequency to the incidentlight frequency. Another near-field transducer is the notch slotwaveguide from microwave circuits applied to optical frequencies (alsoknown as the C aperture). Light polarization may be aligned with thenotch and incident light may concentrate surface charge at the tip ofthe notch.

However, the thermo-mechanical response of the NFT when exposed to suchhigh temperatures has previously led to an undesirable protrusion of theplasmonic structure, thereby causing the NFT to become the minimum flypoint over the medium. This increases the risk of damage to the NFTresulting from disk contact during touchdown and the presence of highthermal asperities during back-off operations. Thus, although minimalclearance (e.g., sub-nanometer clearance) between the head and disk isdesired for high areal density in HAMR HDDs, large variations in NFTprotrusion during operation has made clearance management for previousattempts very difficult.

Previous attempts to protect the NFT against such damage resulting frominteraction between the NFT and the medium have been unable to do sowith a desired amount of efficiency. For instance, attempts topreemptively recess the NFT from the media facing surface of a head haveproven to be difficult to control due to thermal oxidation. Moreover,recessing the NFT undesirably results in requiring higher operatingpower to generate sufficient heat at the medium. In other instances,attempts have been made to implement a passive protection pad to preventa protruded NFT from contacting the medium. However, the extent to whichan NFT protrudes varies greatly during use, thereby making the passiveprotection pad potentially less effective.

In sharp contrast, various embodiments described herein prevent an NFTfrom becoming the minimum fly point over the medium during operation,thereby desirably providing greater reliability during recording.According to some approaches, NFT protrusion may be reduced byselectively implementing underlayers having reduced coefficients ofthermal expansion, as will be described in further detail below.

FIG. 5A depicts a partial cross sectional view of a system 550 having amagnetic HAMR head 500, in accordance with one embodiment. As an option,the present head 500 may be implemented in conjunction with featuresfrom any other embodiment listed herein, such as those described withreference to the other FIGS. Of course, however, such head 500 andothers presented herein may be used in various applications and/or inpermutations which may or may not be specifically described in theillustrative embodiments listed herein. Further, the head 500 presentedherein may be used in any desired environment.

It should be noted that the dimensions of the components illustrated inFIG. 5A may be exaggerated (e.g., larger than would typically beobserved) relative to other components, which are in no way intended tolimit the invention. Moreover, to simplify and clarify the structurespresented, and spacing layers, insulating layers may be omitted from thesubsequent figures and/or descriptions. Thus, although FIG. 5Aillustrates an illustrative cross sectional view of a magnetic HAMR head500, additional and/or alternative layers and combinations of layers maybe used in the structure as would be appreciated by one of ordinaryskill in the relevant art upon reading the present disclosure, includinginsulating layers, adhesion layers, etc. In addition, any of the layersdescribed in relation to head 500 may be comprised of multiple layers,which may or may not be of the same material.

Referring now to FIG. 5A, the head 500 includes a return pole 502 whichis coupled to the main pole 504, a portion of the main pole 504 beingpositioned at the media facing surface. The return pole 502 may includea conventional magnetic alloy or material. Exemplary materials for thereturn pole 502 include Co, Ni, Fe, Cr etc. and/or combinations thereof.Moreover, the main pole 504 may include any known suitable material,such as NiFe, CoFe, CoNiFe, CoFeCr etc.

The head 500 also includes an optical waveguide 506, surrounded bycladding layers 508, 510, 512. In various embodiments, the claddinglayers 508, 510, 512 may include any material which would be apparent toone of ordinary skill in the art, such as Al₂O₃, SiO₂, etc., and/ortheir composites. Moreover, the cladding layers 508, 510, 512 mayinclude same, similar or different materials, depending on the desiredembodiment.

According to the present embodiment, optical waveguide 506 and claddinglayers 508, 510, 512 are adjacent the NFT 523 which is positioned towarda media facing surface 501 of the head 500. As shown, cladding layers508, 510, 512 are adjacent to the waveguide 506 and the waveguide 506 ispositioned behind a side of the NFT 523 farthest from the media facingsurface. However, in other embodiments, the waveguide 506 and/orcladding layers 508, 510, 512 may be offset from the NFT 523 in thetrack direction T, e.g., for embodiments having a nanobeak antenna aswould be appreciated by one skilled in the art upon reading the presentdescription.

Moreover, the waveguide 506 and cladding layers 508, 510, 512 extendaway from the NFT 523 along a direction H perpendicular to the mediafacing surface 501. It should be noted that although three claddinglayers are shown in the present embodiment, any number of claddinglayers may be included, but preferably at least one cladding layer isincluded.

In some approaches, the optical waveguide 506 may be spaced from the NFTby between about 100 nm and about 10 nm, but may be higher or lowerdepending on the desired embodiment. One of the cladding layers 510forms a recess between the waveguide 506 and the NFT 523. Further,cladding layer 510 is also directly adjacent a side of the waveguide506, e.g., extending parallel to a longitudinal axis of the waveguide506 in the height direction H (a direction perpendicular to the mediafacing surface 501). Additionally, another one of the cladding layers512 extends along a leading edge side of the NFT 523, thereby forming aportion of the media facing surface. Thus, in some embodiments, thewaveguide 506 may be positioned adjacent two cladding layers 510, 512,e.g., as illustrated in FIG. 5A.

Optical waveguide 506 preferably extends to the flex side 514 asindicated by the dashed lines. Moreover, the cladding layers 508, 510,512 are illustrated as extending to at least the flex side 514; althoughin other embodiments, some or all of the cladding layers may not extendto the flex side 514. The waveguide 506 extends to the flex side 514having a near field optical source 516, e.g., a laser. The opticalsource 516 emits light, e.g., an optical signal, which is desirablydirected along the optical waveguide 506, toward the NFT 523. Thus thewaveguide 506 is generally used to deliver light energy to the NFT whichcreates a small hot-spot on the surface of the medium 528, therebyinducing isolated heating of the medium 528 surface. The waveguide 506preferably includes a material having a high refractive index (e.g., atleast higher than the cladding layers 508, 510, 512), thereby assistingin keeping the optical signal, emitted from the optical source 516,within the waveguide 506. Illustrative materials for the waveguide 506include, but are not limited to, TaO_(x), TiO_(x), NbO_(x), ZrO_(x),HfOx, etc., and/or their composites. Other exemplary materials for thewaveguide 506 may include Ta₂O₅, and/or TiO₂.

The cladding layers 508, 510, 512 preferably include a material having alow refractive index, e.g., so as to keep the optical signal confinedwithin the sidewalls of the waveguide. In general, a low refractiveindex material may include any material having refractive index belowabout 1.75, but could be higher or lower depending on the desiredembodiment. In other approaches, the low refractive index may be lowerthan the refractive index of the waveguide 506. Illustrative materialsfor the cladding layers 508, 510, 512 include refractive oxides such asAlO_(x), SiO_(x), etc. or other conventional materials having adesirably low refractive index.

As shown, the waveguide 506 may have an approximately uniform crosssection along its length. The thickness of the waveguide 506 may benominally between about 200 nm and about 400 nm, but is preferablythicker than the aperture 524.

However, as well known in the art, the waveguide 506 may have a numberof other possible designs including a planar solid immersion mirror orplanar solid immersion lens which have a non-uniform core cross sectionalong the waveguide's length. Thus, according to various approaches, thewaveguide 506 may have any other cross sectional profile as selected byone of ordinary skill in the relevant art, such as a rectangular,square, triangular, circular, etc., cross section.

With continued reference to FIG. 5A, the head 500 also includes writecoils 518 positioned in a fill material 520, e.g., which may be aconventional insulation layer such as alumina. As would be appreciatedby one skilled in the art, the write coils may assist the head 500 inperforming write operations by inducing a magnetic field in the returnpole 502 which is transferred to the main pole 504 and concentrated in amagnetic lip 522 which is used to write to a magnetic medium 528 (e.g.,a magnetic disk) spaced therefrom. In other words, the magnetic lip 522may serve as a write pole. Thus, the magnetic lip 522 is preferablymagnetically coupled to the main pole 504, and the return pole 502. Inother embodiments, the main pole 504 may have a step formed near thelower portion of the main pole 504.

It is also preferred that the magnetic lip 522 has a straight andsubstantially vertical (perpendicular to the plane of deposition) backedge 521, e.g., farthest from the media facing surface of the head 500.Various methods of forming the magnetic lip 522 capable of achieving asubstantially vertical back edge 521 may be implemented to manufacturehead 500, as would be appreciated by one skilled in the art upon readingthe present description.

Additionally, the NFT 523 is illustrated in the present embodiment asincluding an aperture 524 (e.g., a C aperture) and a conductive metalfilm main body 526 therebelow, which is in no way intended to limit theinvention. Rather, it should be noted that NFT 523 may be of anyconventional design, such as an E-antenna, a lollipop, triangular,nanobeak, etc. According to one approach, the aperture 524 may includeSiO₂.

Looking to the media facing surface view in FIG. 5B, the main body 526is shown as having a notch 527 extending therefrom. The aperture 524 isillustrated as having a “C-shaped” structure, formed by the conductivemetal film main body 526 and notch 527 therebelow. However, depending onthe desired embodiment, the conductive metal film main body 526 may haveany shape. According to one example, the conductive metal film main body526 may have a circular cross sectional shape with a notch extendingtherefrom, e.g., as would be appreciated by one skilled in the art as a“lollipop antenna.” It follows that the NFT 523 may be part of anE-antenna, a nanobeak antenna, a lollipop antenna, etc., depending onthe desired embodiment.

It follows that the partial cross sectional view of the head 500 in FIG.5A and the media facing surface view of the head 500 shown in FIG. 5Bare in no way meant to limit the structure of the NFT as describedherein. Moreover, the process of forming an exemplary NFT structure mayinclude conventional processes which would be apparent to one skilled inthe art upon reading the present description.

Referring still to FIG. 5A, the aperture 524 and conductive metal filmmain body 526 of the NFT 523 may be used to assist in performing writeoperations. As described above, an NFT may be used to heat the magneticmedium, thereby softening the magnetic stability of the magnetic grainsthereof. The energy to heat the magnetic medium may be supplied to theNFT 523 from the optical source 516 via the waveguide 506. In preferredembodiments, this allows for the magnetic field concentrated at themagnetic lip 522 to influence the magnetic orientation of the magneticgrains on the medium 528, e.g., to perform a write operation. Therefore,it is desirable that the NFT is located adjacent the magnetic lip 522,e.g., as illustrated in FIG. 5A.

However, as the NFT 523 is used to heat the magnetic medium, e.g., whileperforming HAMR, heat is also transferred to the NFT 523 itself andsurrounding layers of the head 500, thereby causing them to expand. Asmentioned above, the thermo-mechanical response of the NFT when exposedto such high temperatures has previously led to an undesirableprotrusion of the plasmonic structure, thereby making the NFT theminimum fly point over the medium during use. This increases the risk ofdamage to the NFT resulting from disk contact during touchdown and thepresence of high thermal asperities during back-off operations. Thus,although minimal clearance (e.g., sub-nanometer clearance) between thehead and disk is desired for high areal density in HAMR HDDs, largevariations in NFT protrusion during operation has made clearancemanagement for previous attempts significantly difficult.

Previous attempts to protect the NFT against such damage resulting frominteraction between the NFT and the medium have significantdisadvantages. However, in sharp contrast to previous designs, some ofthe embodiments described herein are able to reduce NFT protrusionrelative to other portions of the writer by selectively implementingunderlayers having reduced coefficients of thermal expansion. As aresult, the amount of thermal expansion experienced at the media facingsurface by the NFT may be selectively reduced, thereby preferablycausing the media facing surface at the NFT to exhibits less thermalprotrusion toward a magnetic medium than another portion of the mediafacing surface, as will be described in further detail below.

Referring still to head 500, an underlayer 530 is preferably included atand/or behind the NFT 523 with respect to the media facing surface 501.As will be described in further detail below, the underlayer 530preferably has one or more materials having a low coefficient of thermalexpansion, e.g., at least with respect to that of the fill material 520.Thus, by positioning the underlayer 530 at and/or behind the NFT 523,some of the embodiments may effectively reduce the amount of thermalexpansion experienced at and/or near the NFT 523. As a result, this maydesirably result in the NFT 523 exhibiting less thermal protrusiontoward a magnetic medium than another portion of the media facingsurface 501, such as the main pole tip and/or return pole tip.

Underlayer 530 is preferably positioned such that the NFT 523 is atleast partially sandwiched between the underlayer 530 and the mediafacing surface 501. Thus, as shown in FIG. 5A, underlayer 530 is atleast partially aligned with, and positioned behind, the NFT 523 withrespect to the media facing surface 501. Accordingly, the underlayer 530may surround at least a portion of the waveguide 506 and/or the claddinglayers 508, 510, 512 in some approaches, e.g., as shown in FIG. 5A.However, as mentioned above, the waveguide 506 and/or cladding layers508, 510, 512 may be offset from the NFT 523 along the track direction(e.g., for embodiments having a nanobeak antenna). Thus the underlayer530 may be offset from the waveguide 506 and/or the cladding layers 508,510, 512, such that the underlayer 530 is positioned at and/or behindthe NFT 523.

The underlayer 530 may further surround at least a portion of the NFT523 in some approaches. Thus, at least a portion of the underlayer 530may extend to the media facing surface 501, e.g., as shown in FIGS.5A-5B. However, in other embodiments, the underlayer 530 may be slightlyoffset from the NFT 523 along the height direction H.

Therefore, it should also be noted that although the underlayer 530 isshown in FIG. 5A as extending away from the NFT 523 along the heightdirection H to the return pole 502 (at the yoke), the underlayer 530 mayextend beyond the return pole in some approaches, or may not extend allthe way to the return pole 502 in other approaches. The underlayer 530preferably has a height of less than about 15 microns, e.g., 10 microns,measured in the height direction H. Moreover, the underlayer 530 mayhave a width of less than about 2 microns, e.g., 1 micron, measured in adirection perpendicular to a plane formed by the intended direction ofmedia travel and the height direction. The underlayer 530 alsopreferably has a thickness of less than about 5 microns, more preferablyless than about 4 microns, e.g., 2 microns, measured along the trackdirection T, but may be thicker depending on the desired embodiment. Forexample, portions the underlayer 530 may have a thickness of greaterthan 5 microns in embodiments having a waveguide and/or cladding layersoffset from the NFT, such as in embodiments having a nanobeak antenna.Moreover, the underlayer 530 may be formed using sputtering, masking,milling, etc., or other conventional processes which would be apparentto one skilled in the art upon reading the present description.

As shown in the present embodiment, fill material 520 has been depositedsuch that it surrounds a number of components of the head 500, includingthe write coils 518. Additionally, fill material 520 is positioned in aspace defined between the return pole 502 and the main pole 504. Thus,the fill material 520 may at least partially surround the underlayer530, the waveguide 506 and cladding layers 508, 510, 512.

As described above, the underlayer 530 preferably has a lowercoefficient of thermal expansion than the fill material 520. Thus,during operation of the head 500, the underlayer 530 will expand lessthan the fill material 520, thereby preferably causing the media facingsurface 501 at the NFT 523 to exhibit less thermal protrusion toward amagnetic medium 528 than another portion of the media facing surface501, e.g., affected by the higher amount of thermal expansionexperienced by the fill material 520. As a result, the reduced thermalexpansion experienced by the underlayer 530 prevents the NFT 523 frombecoming the minimum fly point over the medium during operation, therebydesirably providing greater reliability during recording. Again, it ispreferred that the underlayer 530 is positioned at and/or behind the NFT523. In other words, it is preferred that the underlayer 530 is presentin an NFT region which at least partially surrounds the NFT 523 and/orextends behind the NFT 523 in the height direction H.

The inventors also discovered that implementing an underlayer 530 havinga higher thermal conductivity than that of the fill material 520 mayprovide additional performance improvements. Materials having higherthermal conductivity are able to better dissipate the heat, therebyallowing underlayer 530 to more effectively diffuse the heat generatedat the NFT 523 during use, and further reduce the amount of thermalprotrusion experienced by the media facing surface 501 at about the NFT523.

According to an exemplary approach, fill material 520 may includealumina and/or other conventional insulation materials. Moreover,depending on the desired embodiment, underlayer 530 preferably includesone or more materials having a low coefficient of thermal expansion,such as fused silica (e.g., amorphous fused silica), aluminum nitride,silicon nitride, silicon carbide, etc. Underlayer 530 also preferablyhas a higher coefficient of thermal conductivity than that of the fillmaterial 520, e.g., which may be alumina. Table 1 below illustrates thedifference between the coefficient of thermal expansion for aluminacompared to that of exemplary underlayer materials. The coefficient ofthermal conductivity is also shown for each of the respective materials.

TABLE 1 Thermal Thermal Conductivity Underlayer Material Expansion10⁻⁶/° C. W/m · °K Alumina (Al2O3) 8.1 18 Fused Silica (SiO2) 0.55 1.38Aluminum Nitride (AlN) 4.5 140-180 Silicon Nitride (SiN) 3.3 30 SiliconCarbide (SiC) 4.0 120

As shown, the coefficient of thermal expansion for alumina is muchhigher than each of the coefficients of thermal expansion for fusedsilica, aluminum nitride, silicon nitride and silicon carbiderespectively, thereby illustrating the difference in thermal expansionexperienced by the different materials. Additionally, the thermalconductivity coefficient of aluminum nitride, silicon nitride andsilicon carbide is greater than that of alumina, thereby providing agreater amount of heat dispersion than alumina. It should also be notedthat the specific underlayer materials listed herein are in no wayintended to limit the invention.

Looking to FIG. 6, a graph 600 illustrates the thermal protrusionexperienced at different points along media facing surfaces of twodifferent magnetic heads at different laser energy levels. It should benoted that the results illustrated in graph 600 were gathered frommodeling and are in no way intended to limit the invention.

As shown, the maximum protrusion, which directly corresponds to theminimum fly point over the medium, for a magnetic head without anunderlayer and exposed to 16 mW is at the NFT. In other words, themaximum amount of thermal protrusion experienced by the media facingsurface of the magnetic head without an underlayer is undesirably at theNFT. Conversely, after adding an underlayer having fused silica, theminimum fly point for the magnetic head shifts to a different portion ofthe media facing surface when exposed to the same energy level of 16 mW.In other words, adding a fused silica underlayer caused the NFT toprotrude less, and thereby be recessed with respect to a differentportion of the media facing surface experiencing a greater amount ofthermal expansion, e.g., caused by the fill material having a highercoefficient of thermal expansion than the underlayer. As a result, theNFT is protected from damage during use, e.g., while writing to amagnetic medium.

Moreover, similar results were obtained when modeling the exposure ofthe same two head designs to a higher energy level of 24 mW. It followsthat by implementing an underlayer having a coefficient of thermalexpansion which is lower than a surrounding fill material, the NFTremains protected under a range of operating conditions, e.g., lightenergy levels. Operating temperatures of the NFT and surroundingmaterials may vary greatly during use, and various embodiments describedherein desirably ensure continued protection for the NFT despite suchfluctuations in operating temperatures, which was not previouslyachievable, e.g., by pre-recessing the NFT region of the media facingsurface.

Although preventing the NFT from becoming the minimum fly point over themedium during operation is desired to avoid head-disk interference(HDI), it is also preferred that the NFT does not become over recessedfrom the medium. As the NFT is moved farther away from the medium, theNFT has less of an effect on the magnetic medium as there is moreseparation between the NFT and the target (the focused spot on themedium). Thus, the protection afforded by recessing the NFT from theminimum fly point may be weighed against the corresponding loss of writedetail when determining a desired amount of separation between the NFTand the medium. However, it is preferred that the NFT 523 is at leastrecessed enough to prevent it from becoming the minimum fly point overthe medium during operation.

According to an exemplary in-use embodiment of the magnetic head 500having an underlayer structure which is at least partially surrounded byfill material in FIG. 5, which is in no way intended to limit theinvention, light (e.g., an optical signal) may be applied to the NFT 523positioned toward a media facing surface 501 of the magnetic head 500.The light may originate from the optical source 516 (e.g., a laser)which desirably emits the light such that it is directed along theoptical waveguide 506, toward the NFT 523.

As a result of being illuminated by the light delivered by the waveguide506, the NFT 523 creates a small hot-spot on the surface of the magneticmedium 528, thereby inducing isolated heating of the medium 528 surface.However, the NFT 523 itself and surrounding materials are also heated bythe light energy during operation, thereby leading to protrusion of themedia facing surface 501 as a result of thermal expansion. Underlayer530 helps disperse heat away from the NFT 523 while also minimizing theamount of thermal expansion experienced by the media facing surface 501at the NFT 523.

It follows that various embodiments described herein may be able toprovide added protection for an NFT during operation. By optimizing thesize and material properties of one or more underlayer positioned atand/or behind the NFT, protrusion thereof at the media facing surfacemay be selectively reduced. Moreover, reducing the amount of thermalexpansion experienced at about the NFT prevents the NFT from becomingthe minimum fly point over the medium during operation, therebydesirably providing greater reliability during recording. Furthermore,implementing materials having increased thermal conductivity at and/orbehind the NFT may further improve performance of a magnetic head.

Moreover, any of the approaches described and/or suggested herein may beimplemented in embodiments having nanobeak antenna configurations oftypes known in the art. Thus, process flow(s) similar to and/or the sameas any of the embodiments included herein may produce desirableperformance results for nanobeak antennas. Further still, variousapproaches described and/or suggested herein may be implemented inembodiments having front and/or back edge profiles of an NFT antennawhich are different than that of a magnetic pole.

It should be noted that methodology presented herein for at least someof the various embodiments may be implemented, in whole or in part, incomputer hardware, software, by hand, using specialty equipment, etc.and combinations thereof.

Moreover, any of the dimensions described herein with regard to any ofthe FIGS. and/or any other embodiment thereof, may be higher or lowerthan the values listed, depending on the particular sizes and shapes ofcomponents in such particular embodiments.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A magnetic head comprising: an underlayer; a nearfield transducer between the underlayer and a media facing surface; anda waveguide configured to direct energy from a light source to the nearfield transducer, wherein the waveguide is at least partially surroundedby a cladding layer; and wherein the underlayer surrounds at least aportion of the waveguide and the cladding layer.
 2. The magnetic head ofclaim 1, wherein the near field transducer comprises an aperture and amain body, and wherein the near field transducer occupies a portion ofthe media facing surface.
 3. The magnetic head of claim 2, wherein theaperture is C-shaped.
 4. The magnetic head of claim 1, wherein theunderlayer surrounds at least a portion of the near field transducer. 5.The magnetic head of claim 1, wherein a portion of the underlayerextends to the media facing surface.
 6. The magnetic head of claim 1,wherein the underlayer has a height of no more than fifteen microns in adirection that is perpendicular to the media facing surface.
 7. Themagnetic head of claim 1, wherein the underlayer has a thickness of nomore than five microns in a direction parallel to the media facingsurface.
 8. The magnetic head of claim 1, wherein the underlayer has awidth of no more than two microns in a direction that is perpendicularto the media facing surface and perpendicular to a direction of mediatravel.
 9. The magnetic head of claim 1, further comprising a fillmaterial at least partially surrounding the underlayer, the waveguide,and the cladding layer.
 10. The magnetic head of claim 9, wherein theunderlayer has a lower coefficient of thermal expansion than the fillmaterial.
 11. The magnetic head of claim 9, wherein the underlayer has ahigher coefficient of thermal conductivity than the fill material. 12.The magnetic head of claim 1, wherein the cladding layer comprises afirst cladding layer that extends adjacent to a first side of thewaveguide in a direction perpendicular to the media facing surface, andwherein the first cladding layer forms a recess between the waveguideand the near field transducer.
 13. The magnetic head of claim 1, whereinthe cladding layer comprises a first cladding layer that extendsadjacent to a first side of the waveguide in a direction perpendicularto the media facing surface, and wherein a portion of the first claddinglayer extends along a side of the near field transducer and forms aportion of the media facing surface.
 14. The magnetic head of claim 1,wherein the underlayer comprises at least one of fused silica, aluminumnitride, silicon nitride, and silicon carbide.
 15. A magnetic headcomprising: an underlayer; a near field transducer between theunderlayer and a media facing surface; a waveguide configured to directenergy from a light source to the near field transducer; a claddinglayer at least partially surrounding the waveguide, wherein at least aportion of the cladding layer is between the near field transducer andthe waveguide; and a fill material at least partially surrounding theunderlayer, the waveguide, and the cladding layer.
 16. The magnetic headof claim 15, wherein the underlayer surrounds at least a portion of thewaveguide and the cladding layer.
 17. The magnetic head of claim 15,wherein the near field transducer comprises an aperture and a main body,and wherein at least a portion of the aperture and the main body occupya portion of the media facing surface.
 18. The magnetic head of claim15, wherein the underlayer comprises at least one of fused silica,aluminum nitride, silicon nitride, and silicon carbide, and wherein thefill material comprises alumina.
 19. A data storage system comprising: amagnetic media; and a magnetic head configured to write data to themagnetic media, the magnetic head comprising: an underlayer; a nearfield transducer between the underlayer and a media facing surface; anda waveguide configured to direct energy from a light source to the nearfield transducer, wherein the underlayer surrounds at least a portion ofthe waveguide and the near field transducer.
 20. The data storage systemof claim 19, wherein the magnetic head further comprises a magnetic lipat the media facing surface, wherein the magnetic lip is magneticallycoupled to a pole of the magnetic head, and wherein the near fieldtransducer is adjacent to the magnetic lip.